The present invention relates generally to sewage systems which utilize differential pressures to produce sewage transport through the system as contrasted with the more conventional gravity-operated and positive pressure sewage systems. More particularly, the invention relates to vacuum sewage transport systems and apparatus for controlling the operation of such systems.
As distinguished from conventional simple gravity flow sewage systems, vacuum sewage transport systems necessarily rely upon applied energy. In addition, vacuum systems often require a higher degree of mechanization and operational control than simple gravity flow systems. Nevertheless, gravity and positive pressure systems are not cost effective for many applications, and particularly those involving flat terrain, high water table, unstable soil, and rocky terrain.
In the development of vacuum sewage technology emphasis has been placed upon the need to upgrade the systems to enhance reliability, and to reduce installation, maintenance and service costs. Recently, an even greater emphasis has been directed to a reduction in system energy consumption. An example of progress in these directions is found in applicant's U.S. Pat. No. 4,179,371.
As an early alternative to existing conventional gravity-operated and positive pressure sewage systems, various types of vacuum sewage systems have been proposed. U.S. Pat. No. 3,115,148 issued to S. A. J. Liljendhal describes a vacuum system for separately conveying waste products discharged from water closet bowls, urinals, and like sanitary apparatus, while the waste products, or gray water, from bathtubs, wash basins, sinks, and the like are conveyed by a separate conventional gravity system. Similarly, the U.S. Pat. Nos. 3,730,884 to B. C. Burns, and 4,171,853 to D. D. Cleaver et al., are illustrative of other, more recent, vacuum system developments in the art.
The development of control apparatus technology usable in vacuum sewage transport applications is exemplified in the prior art by patents, such as U.S. Pat. No. 3,662,779 to U. A. Weber et al., which details a pressure control apparatus utilizing a bleed pressure control for a diaphragm, U.S. Pat. No. 3,774,637 to U. A. Weber et al., which describes a diaphragm operated three-way spool valve; U.S. Pat. No. 3,791,397 to G. J. Janu which describes a diaphragm operated pressure sensor; and U.S. Pat. No. 3,777,778 to G. J. Janu which illustrates and describes a two-position liquid level flow controller.
As these prior art patents demonstrate, the trend in the developing technology of vacuum sewage systems, and particularly their control elements, has been toward ever increasing mechanical complexity.
Since the typical installed vacuum sewage system is almost entirely below ground, the control elements of such systems are continuously subjected to the effects of the hostile environment in which they must operate. In particular, this hostile environment will invariably produce relatively low ambient operating temperatures and high atmospheric moisture content. Obviously, these conditions can be expected to produce significant accumulations of water in system control elements as a result of condensation of moist air on cool operating surfaces. Such water accumulations have created troublesome problems in the maintenance of long term reliable operation of vacuum sewage systems. And, at times, the reliability of both the systems, as a whole, and the control apparatus components of the systems have been adversely effected by condensation and its associated problems.
The increasing complexity of the control apparatus developed fo the systems has tended to increase system costs and installation costs, as well as maintenance and service costs. And the developing complexity of the control apparatus components has still further aggravated the effects of the hostile operating environment of the systems.